1. Field of the Invention
The invention relates to smoke alarm devices.
2. Prior Art Discussion
Typically, a smoke alarm device comprises a housing having vents to allow flow of surrounding air into and out of the housing, an alarm indicator means typically including a sound emitter (horn), a smoke sensor, and a control circuit which monitors the sensor output to determine if smoke is present and activates an alarm if smoke is present. The most common smoke sensors are of the optical and ioniser types.
Such smoke alarms have been available for many years and generally work quite effectively. However, there is a need to improve reliability without increasing costs and indeed there is general commercial pressure to progressively reduce costs to encourage the wide availability and use of smoke alarm devices.
Thus, the invention is directed towards providing for improved reliability in smoke alarm devices while at the same time reducing costs.
According to the invention, there is provided a smoke alarm device comprising:
a housing having vents to allow flow of surrounding air into and out of the housing,
an alarm indicator means,
a smoke sensor, and
a control circuit comprising means for monitoring a sensor output, for determining if smoke is present, and for activating the alarm indicator if it is present, characterised in that,
the sensor and the control circuit are integrated together in an integrated circuit mounted within the housing.
In one embodiment, the integrated circuit is an ASIC.
In one embodiment,
the sensor comprises a photo-detector, and
the alarm device further comprises an optical chamber comprising means for blocking ambient light, an internal light source, means for allowing the sensor to detect scattered light within the chamber, and means for allowing surrounding air to flow into the chamber.
In another embodiment, the integrated circuit further comprises a shielding case for the integrated circuit. said case comprising a window to provide a field of view for the sensor.
In one embodiment, the case comprises an integral earth terminal.
In one embodiment, the control circuit comprises means for dynamically adjusting sensitivity in response to sensing of back-scatter arising from dust contamination within the optical chamber.
In another embodiment, said sensitivity adjustment means comprises means for decreasing sensitivity only at least three hours after contamination has reached a sensitivity-decrease threshold level.
In a further embodiment, the sensitivity adjustment means comprises means for incrementing a counter every time contamination above said sensitivity-decrease threshold is detected and means for decreasing sensitivity when the counter value reaches a counter maximum value.
In one embodiment, said sensitivity-decrease threshold level is a proportion of an alarm threshold level which sets the alarm sensitivity.
In one embodiment, the sensitivity adjustment means comprises means for increasing sensitivity in response to contamination dropping below a sensitivity-increase level.
In one embodiment, the sensitivity adjustment means comprises means for increasing sensitivity within one minute of contamination dropping below the sensitivity-increase level.
In another embodiment the sensitivity adjustment means comprises means for increasing sensitivity in successive steps separated by less than one minute.
In one embodiment, the sensitivity adjustment means comprises means for adjusting sensitivity by changing a sensor output alarm threshold level.
In one embodiment, the sensitivity adjustment means comprises means for automatically setting the sensitivity at the least sensitive level on power-up.
In one embodiment, the control circuit comprises means for generating a user output indicating that the optical chamber needs to be cleaned if the contamination reaches a warning level.
In anther embodiment, said user output is a flashing LED.
In one embodiment, the control circuit comprises means for storing a flag when smoke is detected, and for subsequently, after the smoke has cleared, generating a memory indication that smoke was sensed.
In one embodiment, the control circuit comprises means for generating the memory indication in response to user testing of the device.
In one embodiment, the alarm indicator means comprises a sound emitter, and the memory indication is activation of the sound emitter at a different frequency than for indicating that smoke is being sensed.
In one embodiment, the control circuit comprises means for resetting the flag upon testing.
In another embodiment, the control circuit comprises an interconnect interface, and means for directing the interface to transmit a signal on an interconnect line for a time duration after it has stopped activating the alarm indicator means.
In a further embodiment, the control circuit comprises means for counting occurrences of a photo detector output exceeding an alarm threshold, and for activating an alarm mode when the count reaches a pre-set value.
In one embodiment, the control circuit comprises means for sampling light at periodic intervals and for decreasing said intervals after the first occurrence of the output exceeding the alarm threshold.
According to another aspect, the invention provides a smoke alarm device comprising:
a housing having vents to flow of surrounding air into and out of the housing, an alarm indicator means,
a smoke sensor, and
a control circuit comprising means for monitoring sensor output, for determining if smoke is present, and for activating the alarm indicator if is present, characterised in that,
the sensor and the control circuit are integrated together in an ASIC,
the sensor is a photo detector and the ASIC is connected to an optical chamber whereby the photo detector can sense scattered light caused by smoke present within the optical chamber, and
the ASIC comprises means for comparing an output of the photo detector with an alarm threshold 11, with a sensitivity-decrease threshold, and with a sensitivity-increase threshold, and means for
activating the alarm indicator means if a sensitivity level exceeds the alarm threshold level, for automatically decreasing sensitivity if the photo detector output exceeds the sensitivity-decrease level a pre-set number of times over a period exceeding three hours, and for automatically increasing sensitivity if the photo detector output is lower than the sensitivity-increase threshold within less than one minute.